Small diameter induction heater having fluid cooled coil



Jan. 27, 1970 k. HURST 3,492,453

SMALL DIAMETER INDUCTION HEATER HAVING FLUID COOLED COIL Filed Sept. 17, 1968 3 Sheets-Sheet 1 8 (D J l I o :5! g H EI 1 1 '1 g a! 5 1g 8 i J (\l 1 z 5 i I MY I A 5 i I! v I J 1i i Q FT F m a. Q

7g 3 a s 5 INVENTOR.

KENNETH HURST Q BY ATTORNEY K.'HURST Jan. 27, 1970 SMALL DIAMETER INDUCTION HEATER HAVING FLUID COOLED COIL 3 Sheets-Sheet 2 Filed Sept. 17, l

INVENTOR.

KENNETH HURST ATTORNEY Jan. 2-7, 1970 K. HURST 3,492,453

SMALL DIAMETER INDUCTION HEATER HAVING FLUID COOLED COIL Filed Sept. 17, 1968 3 Sheets-Sheet a FIG. 4

I027 I i E? M L I |so I IZGA V i" FIG. 3

INVENTOR.

KENN ETH HURST ATTORNEY United States Patent 3,492,453 SMALL DIAMETER INDUCTION HEATER HAVING FLUID COOLED COIL Kenneth Hurst, Chattanooga, Tenn., assignor to Combustion Engineering, Inc., Windsor, Conn., a corporation of Delaware Filed Sept. 17, 1968, Ser. No. 760,333 Int. Cl. H05b 5/00, 9/00, 9/02 US. Cl. 21910.49 8 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION In the fabrication of heat exchangers of the shell and tube type, especially those employed for use as vapor generators in nuclear power plants, it is the practice to assemble large numbers of closely spaced, small diameter tubes, within a containment shell. In plants of increased capacity currently under construction and being contemplated, the vapor generators employ several thousands of tubes of about inch in diameter. Assembly of these tubes within the shell is effected by inserting the ends of the tubes into holes provided in a tube sheet that is formed as an integral part of the shell. The tubes are mounted to the tube sheet by expanding their ends into tight engagement within the walls of the holes.

Not infrequently, one or more of the tubes may become damaged during fabrication of the unit and after they are mounted in the tube sheet. When this occurs it has been the practice to replace the affected tube by severing its free portion from the end which is mounted in the tube sheet and thereafter remove the confined end from the tube sheet by drilling. It occassionally happens, however, that a damaged tube is not discovered until after several tube rows have been subsequently installed thereby preventing the removal of the affected tube without first removing a number of the later installed tubes in order that access to the damaged tube by a cutting tool can be had. In such cases it is normally found to be more desirable to merely plug the ends of the damaged tube and operate the heat exchanger at a slightly reduced capacity.

It has long been known that when problems such as these occur in heat exchangers employing tubes of greater diameter, the tubes can be dissassembled from the tube sheet by inserting a heater such as an inductor coil into the mounted tube end in order to impart induced expansive forces on the tube material which, due to the fact that the tube cannot radially expand within the tube sheet will generate high stresses in the tube material. If the generated stresses exceed the yield stress of the tube material the material will be caused to expand axially such that, upon cooling, the tube will contract to a diameter sufiiciently small to permit easy disassembly of the tube from the tube sheet.

This method of tube removal has been prevented where tubes having as small a diameter as those employed in nuclear vapor generators are used due to the fact that induction heaters heretofore known in the art possesses too 3,492,453 Patented Jan. 27, 1970 great a diametral dimension to be inserted into tubes of less than approximately one inch. The diameter of such heaters is dictated, in part, by the fact that they are manually operated and therefore, must employ completely insulated power connections. Moreover, means must be provided to pass a coolant in heat exchange relation with the inductor coil in order to prevent damage of the apparatus caused by overheating. In so-called compact heaters of the prior art this feature has been accomplished by employing inductor coils that are tubular and through which the cool liquid can be circulated. The use of tubular coils, however, adds measurably to the diameter of the heater thereby preventing their use as heaters of the type required by the instant application.

It is, therefore, a principle object of the present invention to provide a compact induction heater having sufficiently small diametral dimensions to be capable of being inserted into small diameter tubes of the order of inch or less.

SUMMARY OF THE INVENTION According to the invention there is provided induction heating apparatus particularly adapted to be inserted within elongated, small diameter tubes that are mounted in tube sheets in order to heat the confined ends of these tubes. The apparatus includes a heater assembly comprising a pair of concentrically spaced tubular members housed within a ceramic casing. An axial extension of the inner of the two members extends beyond the outer member and mounts a ferrite ceramic bushing about which a solid wire inductor coil is wound. The tubular members are formed of electrically conductive material and are mutually insulated so as to define a current path for supplying power to the inductor coil while the concentrically spaced disposition of the members within the casing defines a coolant flow passage by means of which a cooling liquid can be circulated through the apparatus to prevent over-heating thereof. The invention further includes mechanisms operative to drive the heating apparatus within the tubular workpiece whereby uniform heating of the tube material confined within the tube sheet can be effected.

DESCRIPTION OF THE DRAWINGS FIGURE 1 is a side elevation of induction heating apparatus of the present invention including motor drive means therefor operatively associated With tubes mounted in a tube sheet;

FIGURE 2 is a sectional elevation illustrating the indulction heating apparatus of the present invention in deta1 FIGURES 3 and 4 respectively are a sectional elevation and plan view of the motor drive means employed in the disclosed embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIGURE 1 of the drawings for the purpose of description, one mode of induction heating apparatus, indicated generally as 10, is illustrated together with its associated mechanism. In the drawing the induction heating apparatus 10 is shown as being operatively connected to an associated drive mechanism, indicated as 12, that enables the heater apparatus to be applied to the interior of one of a number of small diameter tubes 14 that are mounted in tube holes 16 provided in the tube sheet 18 of a shell and tube type heat exhanger. In this application the induction heater apparatus 10 is effective to enable disassembly of a damaged or defective tube 14 from the tube sheet 18 after the former has been mounted in the latter by means of the radial expansion of the end of the tube into tight fitting engagement with the interior surface of the tube holes 16 in the tube sheet. Disassembly is achieved by employing the induction heater to apply heat to the interior of the tube 14 along that portion of its length that is enclosed within the tube sheet 18 for the purpose of imparting thermally induced stresses to the tube material in excess of its yield stress such that the tube, upon cooling, will contract to a diametral dimension that is less than that of the tube hole 16 whereby the tube can then be readily withdrawn from the hole.

The induction heater apparatus 10 includes in general, a body portion, indicated as 20, and a heater portion, indicated as 22, the apparatus, as illustrated, being operatively connected to the associated drive mechanism 12. The body portion 20 of the apparatus comprises front and rear, generally cylindrical body members, 26 and 28 respectively, that are fabricated ofelectrically conductive material and that are mutually spaced from one another by means of an electrical insulator spacer 30 interposed between the two members. As shown, the front body member 26 is provided at its leading end with an integrally formed cylindrical extension 32 having external threads adapted to attach an internally threaded insulator cap 34 and packing member 35. The extension 32 possesses an external diametral dimension that is somewhat less than that of the remainder of the member 26 so as to provide an annular shoulder 36 that operates to mount an insulated housing sleeve 38 which encloses the assembled body members 26 and 28 and spacer 30. The rear end of the sleeve 38 is formed with an internally threaded opening adapted to connect insulated adapter plug 40 that completes the external insulation of the body portion 20 and which serves to connect the induction heater apparatus 10 to the drive mechanism 12 as hereinafter described.

Means are provided in the body portion 20 to mount the heater portion 22 in a way as to enable the supply of electrical current and cooling fluid thereto. As shown, the interior of the front body member 26, including its axial extension 32, is provided with an axially disposed throughbore having three longitudinally spaced portions indicated as 42, 44, and 46 respectively and each being formed with increasing diameters from rear to front of the member. The spacer 30 is centrally apertured, as at 48, and the rear body member 28 contains an axial bore 50 which extends only part way therethrough, the aperture 48 and bore 50 being sized and located to conform with a through opening provided in insulation bushing 51, the latter being disposed in bore 42 of the front body member 26.

The housing sleeve 38, at 52, and both body members 26 and 28, at 54 and 56 respectively, are provided with radial apertures to receive a pair of threaded nipples 58 and 60 that communicate with the bore 50 in the rear body member 28 and bore portion 44 in front body member 28 respectively. The nipples 58 and 60 are formed of electrically conductive material and connect by means of electric leads, indicated generally at 62, with a source of high frequency electrical power 64 to supply electric current to the inductor coil of the apparatus. The nipples 58 and 60 are internally bored and are connected by means of flexible fluid conduits 66 and 68 to a source of cooling liquid (not shown) whereby circulation of the cooling liquid through the apparatus is effected. In the arrangement shown nipple 58 defines the cooling liquid inlet to the apparatus while nipple 60 defines the cooling liquid outlet thereof.

The heater portion 22 of the apparatus 10 comprises a series of concentrically related tubular members that mount an inductor coil 70 and which are so disposed and arranged as to conveniently effect the supply of electric current to the coil and of cooling liquid in heat exchange relation thereto. Thus, the heater portion 22 includes an external tubular casing 72 that is closed at its leading end and which may be formed of a ceramic material to provide insulating properties to this portion of the apparatus. As shown, the casing 72 has its rear, open end fixedly mounted by any well known means within bore portion 42 of the front body member 26. The casing 72 encloses a pair of concentrically disposed, open ended tubes, indicated as inner tube 74 and outer tube 76, that extend axially through the casing and whose respective rear ends 78 and 80 mount in the bore 50 in the rear body member 28 and bore portion 44 of front body member 26. The tubes 74 and 76 are concentrically spaced by means of insulator bushings 82 and 84 thus to define three concentrically separated fluid fiow passages 86, 88 and 90, that extend through the heater portion 22 with passage 86 communicating with the through-opening in the inlet nipple 58 to form the cooling liquid inlet passage and passage 88 communicating with nipple 60 to form the cooling liquid outlet passage. As shown, the passage 90 between the outer tube 76 and casing 72 communicates with outlet passage 88 by means of a plurality of radial openings 92 circumferentially spaced about the forward end of tube 76. The remainder of passage 90 is a region of liquid stagnation forming a thermal shield to protect the casing 72 against overheating.

The inductor coil 70 is arranged as part of an assembly unit axially disposed adjacent the forward end of the interior casing 72. The unit includes a small diameter, solid wire coil 70 that is helically wound for a number of turns about a bushing 94, formed of powdered insulated particles of magnetic iron. The bushing 94 is concentrically mounted to a short length of tubing 96 formed of electrically conductive material which is received within the forward end of inner tube 74 and which extends beyond the end of the inductor coil 70 to a position slightly spaced from the closed end of casing 72. A tight fit is maintained between the tube 96 and inner tube 74 in order that electric current can be passed along the tubes to the coil which is attached at its ends, 98 and 100 respectively to the ends of tubing 96 and outer tube 76 respectively.

The operation of the induction heater apparatus 10 thus far described is as follows. The heater portion 22 of the apparatus is positioned within the interior of tube 14 to the desired depth of application of heat to the tube material. High frequency currents are supplied to the coil 70 from electric source 64 and flow from the source seriatim through inlet nipple 58, rear body member 28, inner tubes 74 and tube 96 to the coil and then back through outer tube 76, front body member 26 and outlet nipple 60 to complete the electric circuit. These high frequency currents create a magnetic flux field which induces high frequency currents to flow in the tube 14 causing the material to rapidly heat. As current is supplied to the coil 70 the apparatus is withdrawn from the tube 14 at a constant rate in order that the tube 14 will be heated uniformly over that portion of its length that is retained within tube sheet 18. At the same time, overheating of the apparatus is prevented by the circulation of cooling liquid which is maintained for so long as the coil 70 is energized. The path of liquid flow between conduit 66 and 68 and through the apparatus is defined by the series connection of passages consisting of the opening through the inlet nipple 58, bore 50, passage 86 and tube 96 to the interior of casing 72 and thence to passage 90, openings 92, passage 88, bore portion 44 and back to the opening through outlet nipple 60.

In the particular application described, heating the tube 14 along that portion of its length that has been expanded into the tube hole 16 of tube sheet 18 imparts thermal stresses to the tube material in excess of the materials yield stress. These induced stresses cause the tube material to expand axially within the tube hole 16 such that, when the tube is cooled, its end will be contracted to an external diameter that is considerably less than the internal diameter of the tube hole whereupon the tube can be easily withdrawn from the hole.

While the described induction heating apparatus is of a size and nature such that it can be easily manipulated by hand, the disclosed embodiment of the invention includes a drive mechanism 12, the use of which insures movement of the heater within tube 14 at a uniform rate. The drive mechanism 12 includes a frame comprised of parallelly spaced cylindrical rods 102 fixedly mounted between front and rear end brackets 104 and 106 respectively. The front ends of the rods 102 are caused to extend a distance beyond the front bracket 104 and are sized and spaced so as to be received within the ends of tubes 14 mounted within tube sheet 18 adjacent the tube to be worked upon by the heating apparatus. Thus the rods 102 provide guides for the movement of the heating apparatus 10 into and out of the interior of the workpiece tube 14.

The front end bracket 104 of the frame extends between and engages the spaced rods 102 and includes a depending flange portion 108 containing a slightly oversized opening 110 to guidingly pass the heater portion 22 of the apparatus 10. The rear end bracket 106 is attached at the rear ends of members 102 and is adapted further to mount the drive assembly comprising a housing 112 including an electrically operated, constant speed motor 114 having a rotatable drive shaft 115 and pulley 116 that can be selectively engaged or disengaged to the drive shaft by means of clutching mechanism (not shown) operated by turnscrew 117. A drive chain 118, fixedly attached at one of its ends 120 to the pulley 116, is adapted to be wound about the pulley with its free end 122 attached to a mounting bracket 124 on the upper end of a carrier 126 that connects the induction heater apparatus 10. The carrier 126 comprises a body 128 mounting a pair of mutually spaced linear bearings 130 adapted to be received and ride along the members 102. At its lower end the body 126 attaches, through a threaded stud 132, a sleeve 134 having an elipsoidal exterior surface and lock nut 136, the sleeve being adapted to retain a fastener 138 that threadedly attaches the adapter plug 40 and which possesses an opening 140 that conforms to the external surface of the sleeve 134 and thereby permits a degree of angular adjustment of apparatus 10 with respect to the carrier 126.

When attached to the drive mechanism 12, the induction heater apparatus 10 is operated as follows. With the carrier 126 retracted to its rearward most position, defined by the abutment of the linear bearings 130 against the rear end bracket 106, the forward ends of the rods 102 are inserted into the interior of tubes 14 adjacent the tube selected to be heated. The leading end of the heating portion 22 of apparatus 10 can be simultaneously inserted into the selected tube.Thereafter, with the turnscrew 117 set so as to disengage the pulley 116 from the motor drive shaft 115, the carrier 128 is manually slid along the rods 102 in the direction of the front end bracket 104 thereby setting the heater portion 22 of the apparatus 10 within the tube 14 a predetermined distance that conforms to the thickness of the tube sheet 18. For this purpose an adjustable stop 142 may be provided extending between the rods 102 and having a releasable fastener 144 operative to permit adjustment of the length of travel of the carrier 128 along the rods 102. Thereafter the turnscrew 117 is operated to lock the pulley 116 to drive shaft 115, and the motor 114 and power source 64 simultaneously actuated in order to energize the coil 70 and at the same time slowly withdraw the heating portion 22 of the apparatus 10 from the tube 14 by the winding of the chain 118 about the pulley. At the same time power source 64 is actuated cooling liquid is admitted to the apparatusby the actuation of an electrically operated valve (not shown) that may be provided in the inlet conduit 66 between the nipple 58 and source of cooling liquid. Electric current and cooling liquid flow are continued until such time as the carrier 128 has been retracted to its rearward most position against the rear bracket 106 whereupon the flow of electric current and cooling liquid can be terminated.

The present induction heating apparatus has proven extremely satisfactory in heating small diameter tubes over relatively long axial lengths which could otherwise not be operated on any known high frequency induction coils. For this reason it has proven extremely useful in the disassembly of tubes from assembled relation in tube sheets, although it should be understood that the herein disclosed apparatus is equally applicable in other applications where it is desired to employ a induction heater.

It will be appreciated that modifications and illustrations of the invention will occur to others upon reading of this specification and it is intended that all such modifications and alterations be included insofar as they are within the scope of the appended claims.

What is claimed is:

1. Induction heating apparatus for use in heating the interior of small diameter holes in elongated metallic workpieces, said apparatus including a heating portion comprising:

(a) an elongated hollow casing having a closed leading end adapted for insertion into the hole to be heated;

(b) concentrically related tubes formed of electrically conductive material disposed within said casing;

(c) spacer means formed of electrically non-conductive material interposed between adjacent tubes of said tubes to define concentrically disposed first and second fluid passages communicating with the interior of said casing for circulating cooling liquid therethrough;

(d) a solid wire inductor coil helically wound about one tube of said tubes and being connected at its opposite ends between said adjacent tubes;

(e) means connecting said adjacent tubes to a source of high frequency electric current; and

(f) means connecting said fluid passages to a source of cooling liquid.

2. Apparatus as recited in claim 1 including a hollow cylindrical bushing formed of magnetic metal interposed between said inductor coil and said one tube.

3. Apparatus as recited in claim 1 wherein said concentrically related tubes are concentrically spaced from the wall of said casing defining a third fluid passage and the outer tube of said tubes contains radial openings establishing fluid communication between said third fluid passage and one of said other passages.

4. Apparatus as recited in claim 3 wherein said radial openings are disposed adjacent the leading end of said outer tube and a substantial portion of said third fluid passage rearwardly of said openings is a region of fluid stagnation.

5. Apparatus as recited in claim 1 including a body portion mounting said heating portion, said body portion comprising:

(a) a pair of longitudinally aligned front and rear body members formed of electrically conductive material;

(b) an electrically non-conductivespacer interposed between said body members;

(c) means forming concentric bores in said front body member for mounting said casing and the outer tube of said tubes;

((1) axially aligned openings penetrating said front and rear body members and said spacer, the inner tube of said tubes extending through said aligned openings for mounting in said rear body member;

(e) a radially disposed fluid conducting nipple formed of electrically conductive material penetrating each of said body members to establish fluid communication with the respective fluid passages defined by said concentric tubes;

(f) means for circulating cooling liquid through said nipples; and

(g) means connecting said nipples to a source of high frequency electric current.

6. Apparatus as recited in claim 5 including a hollow cylindrical bushing formed of magnetic metal interposed between said inductor coil and said one tube.

7. Apparatus as recited in claim 5 wherein said concentrically related tubes are concentrically spaced from the wall of said casing defining a third fluid passage and the outer tube of said tubes contains radial openings establishing fluid communication between said third fluid passage and one of said other passages.

8. Apparatus as recited in claim 7 wherein said radial openings are disposed adjacent the leading end of said outer tube and a substantial portion of said third fluid 8 passage rearwardly of said openings is a region of fluid stagnation.

References Cited UNITED STATES PATENTS 2,556,236 6/1951 Strickland 21910.79 X 2,759,085 8/1956 Van Speren 2l9l0.49 X

JOSEPH V. TRUHE, Primary Examiner 10 L. H. BENDER, Assistant Examiner US. Cl. X.R. 2l9l0.5l, 10.79 

